reduced to -0 . 1 volt and -60 volts, respe ctively ,
during "key down " conditions.
The key is connected to the KEY 2 terminal on
the RECT B b oard , PB- 1 9 6 8 . When the key is
closed , the base of Q 1 001
( 2SA 733 )
is grounded,
causing Q 1 002
( 2SC3 7 2Y)
to conduct . The b ase of
Q 1 003
( 2SA63 9 )
is thus set to 0 when the transistor
conducts. Under these circumstances, the bias
voltage applied to V 1 6 0 1 , V 1 7o 1 , and V 1 702 places
these tubes in the norm al operating condition .
VOX circuit
A portion of the microphone input signal is
amplified by three stages of Q503
(MC3403 P ) ,
which drive the VOX control gate, Q 504
( SN74LS 1 23 N ) .
The output from pin 1 3 of Q 5 04
is fed to the base o f Q 5 1 2
(2SC 1 3 8 3 ) ,
swit ching the
V OX relay on and off according to the presence
or absence of a speech signal .
A portion of the speaker output i s detected b y
D S IO and D5 1 1
( 1 N6 0 ) ,
providing a b ucking voltage
which is fed to Q 503 , preventing the speaker output
from tripping the VOX .
The VOX delay may be set by adjusting V R2b for
the desired delay tim e .
CW SIDETONE
CW side tone o scillator Q5 1 1
(2SC3 73 )
oscillates
at a frequency of approxim ately 800 Hz. The
output from Q 5 1 1 is amplified by the final audio
amplifier, Q 5 0 1 , for delivery to the speaker. The
output from the sidetone o scillator is also fed to
VOX amplifier Q503 , providing semi-break-in opera
tion for CW.
COMMON CIRCUITS
VFO UNIT (PB- 1 440B-34 20)
A modified Colpitts-type oscillator is used to
generate a 5 .0 - 5 . 5 MHz VFO signal , thus produc
ing a 500 kHz tuning range . The oscillator signal
generated by Q80 1
( 2SC3 7 2Y )
is varied by VC80 1 ,
which is geared to a pre cision-built dial t uning
mechanism . VCso 1 consists o f two sections ; the
sub-blades compensate for the capacitance varia
tion of the main blades, which may result from
extreme temperature change .
Varactor diode Dso 1
( 1 S2209)
may be varied by
tuning L806 , providing ± 2 . 5 kHz offset from the
dial frequency (clarifier) .
The VFO signal is amplified by buffer amplifiers
Qso2
( 2SK 1 9GR)
and Qs03
( 2SC372Y ) ,
and passed
to the PREM IX UNIT .
NB
&
FIX UNIT (PB- 1 96 1 )
Two crystal-controlled channels are provided for
operation with this tran sceiver. The oscillator signal
is generated by Q203
( 2SC3 72Y)
and amplified by
Q204
(2SC372Y ) ,
and delivered to the PREM IX
UNIT. Crystals X20 1 and X2o2 oscillate in the
5 .0 - 5 . 5 MHz range .
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